The present invention relates to engine control systems for internal combustion engines, and more particularly to torque matching in a cylinder deactivation engine control system.
Some internal combustion engines include engine control systems that deactivate cylinders under low load situations. For example, an eight cylinder can be operated using four cylinders to improve fuel economy by reducing pumping losses. Fuel economy improvement of approximately 5-10% can be realized.
To smoothly transition between activated and deactivated modes, the internal combustion engine must produce torque with a minimum of disturbances. Otherwise, the transition will not be transparent to the driver. In other words, excess torque will cause engine surge and insufficient torque will cause engine sag, which degrades the driving experience.
Conventional engine control systems that provide torque smoothing have been based on brake torque and as calibrated spark. Engine control systems using this approach does not account for changes in engine and environmental conditions. This approach also does not meet drivability specifications for maximum torque disturbances allowed during transitions between activated and deactivated modes.
An engine control system and method smoothes torque during transitions in a displacement on demand engine. A torque loss estimator generates a torque loss signal based on torque loss due to at least one of friction, pumping and accessories. A pedal torque estimator generates a desired pedal torque signal. An idle torque estimator generates a desired idle torque signal. A summing circuit generates a difference between the pedal torque signal and the idle torque and the torque loss signals and outputs a desired brake torque signal.
In other features, a first switch selects one of activated and deactivated modes for the torque loss estimator. A second switch selects one of activated and deactivated modes for the idle torque estimator. A position of the first and second switches is based on an operating mode of the engine.
In yet other features, a first summing circuit sums the desired brake torque signal and the torque loss signal for the deactivated mode. A first multiplier multiplies an output of the first summing circuit and an air per cylinder (APC) correction signal to produce a first desired deactivated indicated torque signal. A second multiplier multiplies the output of the first summing circuit and a throttle area correction signal to produce a second desired deactivated indicated torque signal. A second summing circuit sums the desired brake torque signal and the torque loss signal for the activated mode. A third multiplier multiplies an output of the second summing circuit and the APC correction signal to produce a first desired activated indicated torque signal. A fourth multiplier multiplies the output of the second summing circuit and the throttle area correction signal to produce a second desired activated indicated torque signal.
In still other features, a first desired APC estimator estimates a desired deactivated APC from the first deactivated desired indicated torque signal. A second desired APC estimator estimates a desired activated APC from the first desired activated indicated torque signal. A third switch communicates with the first and second desired APC estimators and selects one of the desired deactivated APC signal and the desired activated APC signal based on the operating mode of the engine.
In still other features, a first desired area estimator estimates a desired deactivated area from the second deactivated desired indicated torque signal. A second desired APC estimator estimates a desired deactivated area from the second activated desired indicated torque signal. A fourth switch communicates with the first and second desired area estimators and selects one of the desired deactivated area signal and the desired activated area signal based on the operating mode of the engine.
In still other features, the idle airflow estimator includes an idle air per cylinder estimator that generates idle airflow signals for activated and deactivated modes based on engine rpm and idle airflow. A deactivated idle torque estimator receives the deactivated idle airflow signal and generates a deactivated idle torque signal. An activated idle torque estimator receives the activated idle airflow signal and generates an activated idle torque signal. A fifth switch selects one of the activated and deactivated idle airflow signals based on an operating mode of the engine.